Help with separating fingers on model, absolute beginner
This looks like a job for the Knife tool! (Default shortcut K).
Before you start though you may wish to convert to quads, which are typically easier to work with - select the whole mesh in edit mode (shortcut is A for select-all, usually) and still in edit mode use ctrl-j by default - although just typing quad in the command search function will return Tris to Quads as the second option.  Command search is very useful for when you don't know where to find a command.  F3 should bring it up, though I usually pick the interface mode where it's bound to Space, as I use it often.)
When in edit mode, press K, click where you want the cut to start (it will snap to edges and vertices, and you should probably start from an edge but don't necessarily need to be at any particular spot on that edge) then click at each new point you want.  
It will cut new vertices into the mesh to form that geometry.  If you've pressed Z along the way it will cut all the way through, otherwise it just works on the visible side you're looking at.  
Anyway, make some cuts up the length of the fingers, and you can start cleaning up all the other edges while keeping your new edges.  You will need to make new faces (possibly assigning textures) and probably even move some fingers around a bit to get it ready to rig.
Another useful tool is the Rip command (shortcut V in edit mode), which essentially takes one vertex (or set of vertices/edges/whatever) and rips it into multiple, with the ripped side depending on where your cursor is when you invoke it.  Have a play around with it, see if you need it.  
Together those would be the main two things I would use to split up that mesh.  After that, using F (make face) or alt-F (fill a bunch of faces - sometimes not always reliable but much faster when it works) to fill in the holes you've just made so that the fingers have actual side-faces where they used to be joined, and you should be most of the way there.